Both low density lipoproteins (LDL) and very low density lipoproteins (VLDL) have been implicated as positive risk factors in the genesis of atherosclerosis, whereas high density lipoprotein (HDL) concentration is an independent negative risk factor. Both diabetes and obesity are associated with changes in plasma lipoproteins and these changes may be related to the increased prevalence of cardiovascular disease. We are studying lipoprotein composition in obese and diabetic Pima Indians. Comparison of data on nondiabetic Pimas to those of Caucasians indicates Pima males and females have lower total and LDL cholesterol. Pima males and females have lower HDL cholesterol than Caucasians, and there is no sex difference in HDL in the Pimas. Measurements of total cholesterol and triglyceride and HDL cholesterol were also performed on samples from 2 South Pacific populations - the Polynesians of Rarotonga and the Melanesians of New Hebrides. In both, HDL cholesterol was low, and, as in the Pimas, there were no sex differences in HDL cholesterol. Cholesterol and triglyceride in Raratongans was higher than in the population of New Hebrides, and there appeared to be a relation between the occurrence of hyperlipemia and increased cardiovascular disease (CVD) in Raratonga. The data to date on lipoprotein composition of these various populations suggest there are racial differences in lipoprotein distributions which may be important in the determination of the prevalence of CVD. Diabetes in Pimas was associated with increases in VLDL triglyceride and decreases in HDL cholesterol in both sexes at all ages. Changes in lipoprotein distribution were greater in female diabetics, because LDL cholesterol was increased. Multiple regression analyses indicated that plasma glucose appeared to be the most important determinant of both VLDL and HDL in diabetics.